Attenuation equalizer



May], 1923. 1,453,980

.' R. s. HOYT ATTENUATiON EQUALIZER Filed June 29 1918 3 Sheets-Sheet 1E} I I 1E 1 E v 2 Fzyfl 7 I 1V Equalzzer TV I 'g i is J 4 v 2 4 P 3 f I4 2 Equalizer Line [/2 .INVENTOR. H. SHoyz BY z. m

A TTORNEY 1,453,980 R. s. HOYT ATTENUATION EQUALIZER FiledJune 29 1918 3Sheets-Sheet 5 4 3 4 Laaded Lilw with Mid-110ml Irminatia 4. 9 494 4 $42 sobmzesmadedmm T I W W 0 c c c 'c i' INVENTOR.

ATTOI iNEY A Improvements in Attenuation Patented May 1, 1923.

RAY S. HOYT, OF

BROOKLYN, NEW YORK, ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPHCOMPANY, A CORPORATION OF NEW YORK.

ATTENUATION EQUALTZER.

Application filed. June 29,

To all whom it may concern:

Be it known that 'I, .RAY S. HoY'r, residing at Brooklyn, in the countyof Kings and State of New York, have invented certain.

Equalizers,of which the following is a specification.

This invention relates to transmission systems and more particularly tosystem for the telephonic transmission of speech. Its object is toprovide means whereby the distortion of the received signals,

. ly 200 cycles per second, to 2,500 cycles per particular,

respect to second. It is evident that for clear articu- 'lation of thereceived speech it is desirable that the relative amplitudes oftheseconiponents or harmonics shall be the same in the received wave asin the: transmitted wave. When such a. condition obtains, thetransmitting system is called distortionless. In actual transmissionsystems, however, it is well known that-the distortion with respect tofrequency 'is considerable, and, in when the transmission systemincludes long lines, the distortionmay be very large. The usualcharacter of tion is a diminution of the amplitudes of the highfrequency component currents with the low frequency currents, wherebythe character of the received speech may be so modified as to seriouslyobscure the articulationand clearness of speech.

From the foregoing it will. be clear that ordinarily the requiredfunction of the at-- tenuation equalizer of this invention, is todiscriminate against the low frequency com ponent currents to the endthat the disthis distortype of equalizer;

1918. Serial No. 242,567.

crimination of the actual system against the high frequency componentcurrents shall be substantially neutralized. It will be understood,however, that this invention is not limitedto such'a function since itmay be used also to equalize transmission -over a system whichdiscriminates against its low frequency components. I

Moreover, it will be understood that this invention is not limited to,the function of attaining exact equalization, but the equalizer may besoconstructed as to produce for the resultant system a desired variationof amplitude with respect'to frequency, which departs by'a predeterminedamount fromv the exact equalization heretofore discussed. 5

This maybe accomplished by merely designing the equalizer with respectto an assumed variation in the transmission system proper, which differsfrom the actual variation bythe desired amoun The invention may now bemore fully derstood by reference to scription when read in connectionwith the accompanying drawings. In the drawings, Flgure '1 1s aschematic diagram of a transmission system comprising two sections, saiddiagram being provided in order to assist in understanding thedevelopment of certain general formulae pertaining to transmission;

the following de-;

Fig. 2 is aschematic diagram of the system of Fig. 1 inserted;

Fig. 3 is a schematic with an attenuation equalizer diagram of "a linecircuit with terminating impedances and having an attenuation equalizerinserted therein; Fig, 4 is a diagram of a series impedance Fig. 5 is adiagram of Fig. 4 applied'to a loadedline with midsection termination,that is, toa loaded line whichbeginswith a- I half loading-section, aloading-section being line section equalt'o a showing the equalizer ithe portion-of line existing betweenany'two I succeeding loading coils,

Fig. 6 is a diagram showing a series of v I curves illustrating theattenuation ofthe va-' rious parts of the system of Fig.- 5;

Fig. 7 is a diagram of a shunt impedance 2 type of equalizer;

Fig. 8 is a diagram showing the equalizer of Fig. 7 applied to a loadedline with midload termination, that is, to a loaded line which beginswith a half load coil, a. half load coil being one whose impedance ishalf the impedance of a normal or whole'coil;

Figs. 9 and 10 illustrate two types of pew riodic structures which maybe used as attenuation equalizers;

Fig. 11 is a diagram showing the attenua tion equalizer of Fig. 10applied to a loaded line with mid-load termination; and

Fig. 12 is a diagram showing attenuation curves for the system of Fig.11.

The general theory underlying the attenuation equalizer of thisinvention will now be developed, after which the specific types will bedisclosed and the appropriate design formulae will be derived.

Referring to Fig. 1, a transmission system is schematically represented,which is shown as consisting of two parts I and H connected together atterminals 3, 3. An E. M. F. E is illustrated as impressed be-- tweenterminals 1, 1 and for generality an E. M. F. E between terminals 2, 2.If the current entering terminals 1 is designated by I, and the currentin terminals 2 by 1,, then I, and I, are related to the impressed E. M.F.s. by equations of the form:

1 TIIEI TIZEZ 1 2 zi i zz z (1) In the above expressions T T T and T arethe coefficlents of admittance of the system. T is equal to the currentflowing into terminal 1 of the system when unit E. M. F. is app-liedbetween terminals 1, 1 and terminals 2, 2 are short circuited. SimilarlyT is equal to the current flowing through terminals 2, 2 under the sameconditions.

T is equal to the current flowingv through terminals 2, 2 when a unit E.M. F. is applied to terminals 2, 2 and terminals 1, 1 are shortoirc-uited.

When we are considering transmission from 1 to 2, E is set equal tozero, whence:

' The coefiicient T is the transfer admittance of the system, that isthe ratio of the current received at terminals 2 to the E. M. F. im-

pressed at terminals 1. This coeflicient may be theoretically determinedwhen the system is specified or it may be experimentally measured. Ingeneral, it will be found that v T is a function of the frequency of theimpressed E. M. F.; it is the variation of T with respect to frequencywhich causes the distortion, which it is the object of this in? ventionto eliminate.

Fig. 2 is a diagram of the system of F ig. l with an equalizer,schematically represented, inserted at terminals 3, 3. If we designateby V and V the voltages between terminals 3, 3 and 4. 4 respectively(the arrows associated with the voltages indicating the directions fromlower to higher potentials), by A A A A the admittances of part Lby B 1313 15 the admittanvcs of part II, and by C C C the admittances of theequalizer, the equations of the system are:

Confining our attention to transmission from 1 to 2- and consequentlysetting E equal to zero, the solution of equations (3) gives:

The significance of the admittance is easily seen. Thus, referring toFig. 2, C is equal to the current flowing into terminal 3 of theequalizer when a unit E. M. F. is applied between terminals 3, 3 andterminals 4, 4 are sho-rt-circnitcd. Similarly C is equal to thecurrentflowing thru terminals 4, 4 under the same conditions. is equalto the current flowing thru terminals 4, 4 when a unit l); M. F.isapplied across terminals 4, 4, and terminals 3, 3 are short-circuited.From these definitions the meaning of the other admittancesis selfevident.

If the equalizer is removed in Fig. 2 the equations of the system fortransmission from 1 to 2 are:

Solving the above equations we obtain the following as the transferadmittance of Fig.

aeaeso Now in the actual system the transfer admittance T varies withthe frequency in the equalized system the requirement is that T as givenby shall be substantially constant over the frequency range required forthe telephonic transmission of speech. This result is attained whenequalizer, characterized by the parameters C C C C is so proportionedthat the absolute value of T as given by (5) is substantiallyindependent of the frequency.

If the equalizer consists merely of an impedance Z (which may be asingle element or maybe a combination of elements) in series with theline the equations for transmission from 1 to 2 in Fig. 2 are asfollows:

Solving these equations and notingthat C :C :C C :1/Z we obtain as thetransfer admittance from 1 to 2 the following: I

i which can also be obtained from (5) by substituting c zc b c zl/ztherein. If on the other hand the equalizer consists of an admittance Yin shunt across the line the equations of the systems fortransmissionfrom 1 to 2 are:

i From these equations we may obtain the I If the system which isequalized consists of a transmission line of characteristic impedance Kand propagation constant I i imitclosed by'the inipedances U and U andif the equalizer be inserted between the line and the impedance U asshown in Fig. 3, then where H, V V are the reciprocals of K,

U U respectively, and are therefore admittances.

Equations (12) in so far as these relate to the transmission lineconstant-s, follow.

from well known formulae, on the assumption that the line is so longthat the sendingend current is independent of the receiving wirinanrfiiz If, on the other hand, the equalizer con-.

sists of an admittance in shunt across the line, then by (11) and (12)If further this equalizer is inserted between a resistance. U and a longline (K, I), (see Fig; 3) whose A and B admittances are given by (12),then by reference to (5), (l2), and (15) it will be seen that thetransfer admittance of this system is Neglecting the term which containsthe factor 6 which is commonly ,small, (16) reduces to arm- 5 Seriesimpedance type 0 f equalizer.

Equation (13) may be written eKU, J4KU K U a/eUjU K+ U K+U K+U -+Z It isnow convenient to introduce a set of parameters defined by the followingequa- In the above equations the two elements of each of theexpressionson the left hand side of the equality sign are respectivelythe real and imaginary components of the cora id log urn,

whence, by equations (20),

. In the practically important case considered below, the terminalimpedances U and U are pure resistances and henceconstants whose valuesare independent of frequency.

For such case it follows from (22) that distortion with respect tofrequency will be The specific type of the attenuation equalizer now tobe considered is shown in Fig. 4,

- and consists-of a resistance R in parallel.-

with the serial combination of an induce responding expressions on theright hand side, which latter expressions are in general complexfunctions. Thus, for any transmission system, the attenuationcoefficient A is the real part of the pro agation coefiicient P of thesystem, while 2' is the imaginary component, of which A is arealexpression and 2' denotes the operator 1.

From (19) it follows that wherein a pair of vertical lines enclosing anexpression indicates that the absolute value of such expression ismeant.

From equation (18) it follows that the absolute value of the transferadmittance of the system may be expressed as 445K U K+U K 31: HM (21),tance L and a capacity C. If p "denotes 27cf when f is the frequency,and i denotes the imaginary operator /1, the expression for theimpedance Z is The general design procedure for this t pe of equalizerwill now be laid down. ferring to'formula (22) it is evident that theresultant efi'ective attenuation of the system' is A+b+c+a, and that theequalizer afiects only one eoeficient, namely a. Thecoeflicients A, b,and c are given by formulae (20) and the line constants, whence the sumA-i-b-l-c may be taken as the data of the problem.

highest frequency f, of the range over which equalization is desired, itis evident that the resultant attenuation of the system will have auniform constant value equal to forallfrequencies less than f andfurther that no attenuation will be introduced by Further, if -A +b +0is the value of A+b+c at the quencies.

mental data by aid of formulae (.20), the

first step toward the design is to compute by (24) the values of theattenuation a which the ideal equalizer should furnish over thefrequency-range contemplated. Since the equalizer here considered (Fig.4) is char-- acterized by three independent constants (R, L, 0,) theseconstants can be so-evaluated that the equalizer attenuation willwherein R is known from (26). L is then have its ideal values at threedifferent fre- One of these frequencies, namely ff has already beenassigned; forthe other quency f,, the equalizer impedance should Iequalizer elements as follows: By formula (23) the equalizer two it isconvenient to choose the frequency 0, and a selected intermediatefrequency f,. The ideal values of a for the three frequencies O, 7",, f,will be denoted by a 11 ,01 .Since, by (24), the attenuation a furnishedby the equalizer should be zero at the' frebe zero at that samefrequency. If the equalizer were to be proportioned in accord-' ancewith these values, the equalization would be exact at frequencies 0, fand f However, the frequency zero is unimportant, and exact equalizationat the-frequency f is also of minor practical importance. It has beenfound, therefore, that more satisfactory equalization may be secured bychoosing a value of a slightly different from that for exactequalization at frequency O, and also making the impedance of theequalizer zero' at a frequency 7, which is nearly but not exactly equalto f Having therefore decided on appropriate values of a a, I

R, L, C, are determined impedance, and therefore a, is. zero if Sincethis is to be zero at frequency f we have:

Led amp 25 1 At zero frequency the impedancev of the' equalizer issimply It; therefore, by (20) R 1 TI'G QO when K+U, is the value'of-K+U, at-

and i the values of the' Byformulae 23 and" 25 the impedance 2 Z of theequalizer at frequency f zp /2'n 1s Z R1 (fl/far] 1 QT SVHRO Hence, byformulae (20),

' f1/fa) P1l( 1)1i 1 1 where (K+U,) is the value of (K -FL 1) atfrequency f,. Solving this equation for C, in the practically importantcase for which (K+U,) .is pure resistance, we have determined from (25),which gives L:1/C(2 1rf (28) 'Desz'gn of series impedance type ofequalizer for a specific ease.

The equalizer of Fig. 4.- will now be designed in accordance with theforegoing formula to equalize transmission over the system shown in Fig.5, the system consisting of periodically loaded transmission line withterminal impedances U and U which are pure resistances of 1540 ohmseach. The line is terminated at mid shunt (that is, mid-section)position and has the following specifications: Wire..'...'........#19B.&S.gauge.

Cap. per mile .064 10- iarads.

Resistance per mile. 86 ohms.

Leakage permile Proportional to freguency and equal to 0.896X10- atrequencyBOO.

Load coil inductance .175 hepry.

Length of line. load ng sections, 69.6 miles.

Length of loading section... 1.16m11es.

so i

There uired ran e of fre uencies is from zero to about 2400' cycles persecond. We have then Inductance per section, L .175. Capacity persection, C .0742 X 10-;

Further, L /C 1540.

Since the line is terminated at mid-section, I v

the characteristic impedance is given by:

The results of .a computation of the attenuation of 60 sections of theline by means of the known, formulae for v periodically loaded lines isillustrated in curve 1 of Fig. (6).

( 2) on a larger scale.

Curve (2) of Fig. (6) is a plot. of the required valve of a as given byequa-- 'tion (24:) While curve (3) is a plot of curve a .lse :2650

We have therefore 1- (192072650 21 1920 3250 .0092 X 10 farads.

and finally by formula 28) L= 10/.0092(21r2650) .391 henry.

Curve (4) of Fig. (6) shows the computed attenuation actually furnishedby the equalizer having theabove given values While curve (5) is a plotof the resultant attenuation of the system. Itwill be seen that theattenuation is substantially constant over the required range offrequencies.

In the above specific case the object was to equalize the transmission;that is, to make the resultant attenuation conform to a preassignedhorizontal straight line graph, curve 2 representing the attenuationwhich the equalizer must 'furnish to accomplish this object. If,instead, the object were to make the resultant attenuation conform to aT -r fz 1 defined by the followingv equation of the characterand Thesefollow from (31) and (33), the ad- The design of-the equalizer of Fig. 7will H+V H being the characteristic admittance of f we have esaeeo Henceby formula (26) I R:'(2.054=4t1) (3080):3250 ohms o By formula (27) Ipreassigned curved graph (instead of to a preassigned horizontalstraight line graph) the design procedure would be exactly the same asabove if curve 2 is drawn to repre- I sent the attenuation, which theequalizer must furnish to make the resultant attenuation conform to thepreassigned curved graph. Similar remarks apply, of course, to the othertypes of equalizers described below.

Shunt admittance type of equalizer.

If theequalizer consists of an admittance Y, bridged across the linebetween the sending end admittance V and the line (K, I) closed throughan admittance. V at the receiving end, the transferadmittance is givenby (14), which may be written as the expression for the absolute valueof i the transfer admittance.

Now let the bridged equalizer be as shown" in Fig. 7 and consist of aresistance element R in series with the parallel combination of .aninductance L and a capacity C. The adv mittance Y of this combination is1 a. mama The design procedure is now similar. to that for the seriestype equalizer. Havin selected appropriate values of 0 f a an and, forthe practicalliyl important case in which the admittances and V, arereal,

whence, v

mittance of the equalizer at zero frequency being simply l/R.

now be worked out for the system shown in Figl} 8. This system isidentical with that of ig. 5 except that the loaded line is terminatedat mid-load instead of mid-section position. The formula for thecharacteristic impedance K is then 1/ o/ o1 (f/fy J 07 8 (see equation(4) of Patent No. 1,167,693). Hence the characteristic admittance H is 1I 1540 /1-U 2s00 If we select the same values of the parameters asbefore, namely (t .720 I f,: 1920 a,: .484 f '=2650 I then, bysubstitution of these values in for 'riodic structure or wave mulae(35)(37) We have: I

Owing to the exact mathematical relation obtaining between theequalizers of Figs. (4) and (7), curves 4 and 5 of Fig. (5) are alsovalid for the particular design given above;

Wave-filter type of equalizer.

A third type of attenuation equalizer may be obtained by a specialdesign of the pefilter which is disclosed in patent to Campbell No.1,227 ,113 of May 22, 1917 .[The distinguishing prop erty of thestructure, as fully set forth in the above mentioned specification, isthat of transmitting freely or without attenuation all currents whosefrequencies-lie within a preassigned range or ranges of frequency,

while attenuating currents of 'all' frequencies lying outside saidrangeor ranges. In

the present invention the use made of this" characteristic property isquite distinct from that set forth in the above mentionedspecificatiom'in that in the .,present invention, the wave filter is soproportioned that the attenuation introduced by said filter within therange of telephonic frequencies is complementary to the attenuationintroduced by the transmission system' with which it is cooperativelycombined to the end that the resultant attenuation shall besubstantially constant over the desired range of frequencies.

, In other words use is made of the fact vthat in a periodic structureof the ty e disclosed in the above patent the attenuation does not.-

increase sharply at the cut ofl fre uencyof the band of frequenciestransm tte ,but 1ntively, then, (39) and (40),

creases gradually to a large value, the structure this tioned, to renderloaded linesystems substantially distortionless. r 1

The propagation. constant of the wave filter, or periodic structure, isdetermined by equation(2) of Patent No. 1,227 ,113

l (38) 2 In this equation ances in serieswith and in shunt across theline, respectively; and :Z /Z Furthermore the limiting frequencies offree transmission, here designated by f,- and f as stated in the abovementioned patent are determined by:

Letting 0:21: when f is any frequency and referring to the type of wavefilter in which each section ;,consists of an inductance inseries'withthe lines, 'and an inductance and Z and Z are the imped- "illustrated inFigs; '(9)-and (10) are par- 7 ticularly. adapted, when properly proporecapacity in parallel in shunt across the line as shown in Fig. 9,

Z =tpL 2 1 p L C L 'Y 17; (1,IP?LZCZ) If p and 1),, denote 21d, and 21vf1 1 3 2 I P2=P11/1 +4IL2/L1, I I II If 1/ denotes the ratio f /f zp/pthen by substituting the value given by the first equation of (41) inthe th rd equation of a (40) ,we find that eg -a 2 f equation of (41)gives res so- [12a If 1' denotes the ratio f /f ;p /p the last Thecorresponding equations for the type of filter shown in-Fig. 10 are:

(4 and (46) being identical with (43);

It may be shown that the characteristic impedance of a wave filter whenterminated at mid-series (that is, mid-load) is Fw/ l d 'Y /Q and whenterminated at mid-shunt (that is, mid-section) K /Z Z 1 /4) (48) Formula'(47) for K can be derived in a simple manner by considering in an infi--nitely long Wave'filter, terminating at midseries, the first periodicinterval extending from mid-series to mid-series position. If theimpedance of this filter is denoted by K 5 the impedance of theremaining portion (which is also infinitely long) is equal to and thusthe distant end of the first. periodic interval is closed through animpgdance equal-to K Now the impedance of the system consisting of oneperiodic interval (Z /2, Z Z /2) having its distant end closed (throughan impedance K is clearly some function of this closing impedance K andof the preceding elements Z and Z In fact, as is now evident,

solution is the value, given by (47). F or- -mula (48) for K can beestablished in an analogous manner. u

If the values derived above for Z .Z and m parameters defined byIntroducing a set of the equations c to loge z a I,

7 aresnbstituted in (47) and (48.) the midseries and mid-shuntcharacteristlc lmped- F ances of the filter'of F ig. 9 are respectively:50

LI Elen om/i-w T -l K c; 1 1? e 'w Similarly for the type of Fig. 10,

K a w 7 1 I I I it 1:573 51 K b Von/W r w If the propagation ,constant1" of the periodic structure is denoted by PzB-l-iB when B and B arevboth real, it may be shown, from equations (38) and (43); or and (46),that v Cosh P But A cosh 1" =cosh (B+iB) =cosh B cos-B+'i sinh B sin BNow, if we consider frequencies below the range of 'free transmission(that is, f f so that w 1) the expression (1-|-r 2w (r -1) in the firstequation for coshd" isreal; and consequently, in the second equation forcosh I", the term i sinh lB sin Bf must vanish whence H sinh B sin'Bz0SinceB is finite sin 13' muste u al zero and cos B therefore equalsunity. I onsequently 1-+r 2"u; @0811 B" 7 1 a y (52 05 h Vl-w? 2 r 1where B is the attenuation per section. I If now the filter is to beapplied, as in Fig. 3,'to the case of a transmission line (K, I) withterminal impedances U and U the appropriate formula is (17 which, forthe present purpose, may conveniently be written in the form 1105 i fi i(53 K+K K+ U whence; a 1 15 KMU ea K'+K b 5 innv 1U,+K' Sec me n andremembering that lzA-l-iA' and T'zB-l-iB' so that we see, from equation(53), that T, (A+nB+a+bi-c) a" amt! Th application of these formulaeindesigning the equalizer will be illustrated in connection with thespecific case worked out below.

For the practically important case in which U and U are pure andconstant resistances it follows that the problem involved in the designof the filter type equal:

izer is to make the sum A-l-nB-l-a-l-b-I-e' substantially constant overa specified range of frequencies, since then by equation (57) thetransfer admittance of the equalized system is constant. The lineattenuation A and the line impedance K are data of the problem. Thechoice of the type of filter, its termination (mid-series or midshunt,ordinarily), the number of sections n and the parameters 1),, 1' and vi/ z are at our disposal; 'as are also, inmamy cases, the absolutevalues of the terminal impedances U and U since their absolute valuescan be varied by the choice of sultable transformers, to connect them tothe line and filter respectively. The choiceof these parameters is amatterof englneerlng study and trial and error by aid of the formulaealready developed.

'- The design of the type of filter shown in Fig. 10 to equalizetransmission over the system shown in Fig. 11 will now be worked out. Itis required to equalize transmission between the limiting frequencies200 and 2,000 cycles per second, for a system consisting of 500 inilesof 0 en wire No. 8 B. W. Gr. loaded line. The 'ine has a critical orcut-off frequency f, of 2350 cycles per second, and the value of w m rthe line is 1900. The line is terminated at midload position whencev v]i =1900 /1'- f 2350 (See equation (4) of PatentNo. 1,167,693.)

is shown by curve (1) of Fig. 1-2. This at tenuation curve may betheoretically calculated when the line constants are specified or may beexperimentally determined.

The line attenuation A for the 500 miles In any case it is a datum ofthe problem.

After considering several tentative values, the following values of thedeslgn parameters were adopted:

/L,/O =135 It was also decided to terminate the filter at mid-shuntposition.

By reference to formulae previously do-- rived we have then K= steamycosh B ,Solving these last equations the constants is thus computed forvarious frequencies.

by 51) I i l Its graph as a function of the frequency is shown in curve(2) of Fig. 12. It will be observed that its value issubstantially-constant over the preassigned range from 200 to 2,000cycles per second, and therefore the 4 required equalization oftransmission is accomplished. The

absolute value of the resultant attenuation is considerably increasedbut the loss which is thus introduced by the equalizer may becompensated for by em-- ploying a repeater.

It will be seen that by means of this invention, the distortion due tothe increase in at- 'lLC D tenuation with increase in frequency in agiven transmission system, may be substantially eliminated by insertingin the system an impedance arrangement or network so designed as toincrease the attenuation for the lower frequencies to such extent thatthe resultant attenuation of the system will be sub-. stantiallyconstant over the range of frequencies equalized. While this necessarilyinvolves an increase in the total transmission loss, the loss may bemade up by repeaters.

It will also be obvious that the general principles herein disclosed maybe embodied in many other organizations widely differing from thoseillustrated without depart-.

ing from the spirit of the invention as defined in the following claims.

What is claimed is: q

1. The combination with a transmission line in which the attenuationvaries for different frequencies, of an auxiliary localized networkassociated with said transmission line at a point along its length andso constructed and proportioned that the attenuation therein varies withthe frcquency 1n such a manner that the resultant attenuation .of thecombined system will be substantially equal over a desired range offrequencies.

2. The combination with a, transmission line in which the attenuationvaries for different frequencies, of an auxiliary localized networkassociated with said transmission line at a point along its length andso constructed and proportioned as to increase the attenuation of theless attenuated frequencies to such an extent that all frequencies overa desired range will be transmitted over the combined system withsubstantially the same attenuation.

3. The combination with a transmission line in which higher frequenciesare attenuated more than lower frequencies, of an auxiliary localizednetwork associated with said transmission line at a point along itslength and so constructed and proportioned that lower frequencies areattenuated more than higher frequencies to such extent thatthe resultantattenuationof the combined system is substantially equal .over a desiredrange of frequencies.

4. The combination of a transmission line over which differentfrequencies are trans mitted with different atten'uations, and anattenuation equalizer for the line comprising a localized networkassociated with said transmission line at a point along its'length andwhose elements are so related -to each other and to the line, and soproportioned,

that all frequencies within a desired range are transmitted over theline and attenua tion equalizer with substantially equal attenuation.

5. The combination of a transmission line over which higher frequenciesare transmitted with greater attenuation than lower frequencies, and anattenuation equalizer for the line comprising a localized networkassociated with said transmission line ata are so related to each otherand to the line,

and so proportioned, that lower frequencies are attenuated more thanhigh frequencies to such extent that the resultant attenuation of thesystem is substantially equal'over a desired range of frequencies.

6. In a transmissionsystem, a transmission line over which differentfrequencies are transmitted with different attenuations, and anattenuation equalizer, said attenuation equalizer comprising a localizednetwork associated with said transmission line at a point along itslength and consisting of a plurality of elements, so proportioned and sorelated to each other and to the line, that all frequencies within adesired range will be transmitted over the system with substantiallyequal attenuation.

7. In a transmission system,-a transmission line over which higherfrequencies are transmitted with greater attenuation than lowerfrequencies and a localized attenuation equalizer associated With theline at a point along its length, said attenuation equalizer being soconstructed and. proportioned with reference to the line as to increasethe attenuation of lower frequencies 1 point along its length and whoseelements to such extent that all frequencies within a desired range willbe transmitted over the system with substantially equal attenuation.

8. In a transmission system, a transmission line over which differentfrequencies are transmitted with different attenuation, and

an attenuation equalizer serially connected with the line, saidattenuation equalizer comquencies to such extent that all frequen-- cieswithin a desired range will be transmitted over the system withsubstantially equal attenuation.

10. In a transmission system, a transmission line; and an attenuationequalizer, said attenuation equalizer comprising a localized networkassociated with said transmission line at a point along its length andwhose elements are soproportioned and related to each other and the linethat all frequencies within a' desired range will be transmitted overthe system with substantially equal. attenuation.

11. In a transmission system, a transmission line, and an attenuationequalizer serially connected with said line said attenuation equalizercomprising resistance and inductance elements so proportioned andrelated to each other and the line that all frequencies within a desiredrange will be. transmitted over. the system with substantially equalattenuation.

12. In a transmission system, a transmission line, and an attenuationequalizer serially connected with said line said attenuation equalizercomprising resistance and casired range will be transmitted over thesystem with substantially equalattenuation.

14. In a transmission system, a transmission line the attenuation ofwhich varies 'with frequency in accordance with a .known law, and alocalized networkassociated with said line at a point along its length,said network being so connected and proportioned with respect to saidline as to cause the attenuation'of the system comprising the line andnetwork to vary with frequency in a different predetermined manner.

15. In a transmission system, a transmission line the attenuation ofwhich varies with frequency in accordance with a known law, and anauxiliarynetwork the attenuation of which is predeterminable atdifferent frequencies, said auxiliary network being localized withrespect to the line and so designed and so associated with thetransmission line at a point along the length thereof that the resultantattenuation varies with the frequency in accordance with a predeterminedlaw.

In testimony whereof, I have signed my name to this specification thisQ5th day of June 1918.

